#include<iostream>
using namespace std;
int a[100],b[100];
float sum;

int main(){
	b[1]=1;
	b[2]=2;
	a[1]=2;
	a[2]=3;
	int n;
	scanf("%d",&n);
	for(int i=1;i<=n;i++){
		if(i==1||i==2){
			sum+=a[i]*1.0/b[i];
		}else{
			a[i]=a[i-1]+a[i-2];
			b[i]=b[i-1]+b[i-2];
			sum+=a[i]*1.0/b[i];
		}
	}
	printf("%.2f\n",sum);
	return 0;
} 
